Doctor, doctor : Dr Tom Smith answers your questions

Sun confusion

What is the correct balance in a British summer between sunbathing enough to get our vitamin D needs, yet not risking skin cancer?

It's true that we get much of our body's vitamin D from the sun on our skin. So we do need sunshine. The National Osteoporosis Society states that between May and September we should get in the sun for 10 minutes once or twice a day without sunscreen (which blocks vitamin D production). In those minutes we will produce enough of the vitamin before starting to burn (which is the initiator of skin cancer). If we stay too long in the sun, excess vitamin D breaks down, so lying in the sun on a beach for our two-week holiday doesn't build up our vitamin stores for the winter.

Bad circulation?

I am a 28-year-old woman and believe that I suffer from bad circulation. Blood drains to my hands when they hang down, and to my feet when I stand in the same place for more than a few minutes, leading to swollen, red, mottled legs. I have numb arms if I don't move them for a while and rushes of heat to the front of my feet and toes. I exercise regularly and am not overweight. What can I do?

Your lifestyle suggests that you are fit and healthy. However, your autonomic nervous system - the network of nerves that controls the circulation in your legs and arms - may not be working normally. That is fairly common, and can be checked by your doctor. Do tell him or her about your symptoms: once the diagnosis is made, they can probably be controlled by prescription drugs acting on the nervous system.

Are sweeteners linked to cancer?

I've been using sweeteners in my coffee for years, but recently considered stopping after a colleague suggested links to cancer. Are there any?

The authorities in Europe and the US differ in the sweeteners they allow, based on laboratory testing. Although there have been reports over the years linking artificial sweeteners with various diseases, there's no evidence that they cause harm in humans in the amounts we take in tea or coffee. However, why do you take them? Sweeteners maintain and may even enhance your taste for sweet things. Why not start to enjoy coffee and tea without them? You will soon get used to the new taste, and gradually lose your fondness for excessively sweet foods. Most GPs will tell you that, in their experience, people who indulge in sweeteners tend to lose less weight than those who drink their tea or coffee unsweetened.

Dry-eyed but healthy

I'm 22, have a healthy diet and take exercise. But I have dry eyes which are regularly bloodshot. Prescribed eye drops haven't helped.

Could the clue be in your exercise? Are you regularly dehydrating yourself - ie not drinking enough fluids to compensate for the loss in your sweat, breath and urine? Try extra fluids: drink water when you're not thirsty, for example. If you have truly dry eyes you need to put the drops in every hour or so. You may have chronic conjunctivitis, so tests and perhaps antibiotic or anti-allergic ointment or drops may help. If the dry eyes are linked to a dry mouth, then you may have Sjögren's syndrome, in which other secretions (in the gut, joints and vagina) are also less than they should be. That needs expert advice, so see your doctor again.